In April the WMO announced the Arctic ozone hole had reached record proportions – perhaps even doubling the previous depletion record of 2005, a Nature publication recently added. On the southern hemisphere the story seems much the same.
Earlier this month over Antarctica the 10th lowest ozone concentration was measured: 102 Dobson units, according to their joint release. [Scientists speak of an ozone hole at anything below 220 Dobson.]
Seasonal ozone breakdown over the poles
CFC-induced ozone breakdown has two additional requirements: extremely low stratospheric temperatures – and sunlight. That’s why the ozone layer over the poles is most vulnerable – just after winter, when temperatures 10 kilometers up in the sky can be low enough [<90C] for polar stratospheric ice clouds to form, and the onset of spring adds a little UV radiation to get the catalytic breakdown reaction going.
Once conditions are met, and you have enough of the nasty fluorocarbons floating around, chemical reactions can swiftly burn a hole in the protective layer.
The ozone hole, resuming a crisis
We owe it to watchful atmospheric scientists that by 2011 agriculture is still possible and we are still safe to walk outdoors in the sunshine for hours on end. By intelligence, perseverance and chance the Dutch atmospheric chemist Paul Crutzen realized CFCs could be bad news – and researchers of the British Antarctic Survey found out indeed they were. That was in the eighties – and it was just as likely these few clever minds had not noticed what refrigerating industries were setting in place.
If we had waited it out and kept to business as usual, by now the problem would have become lethal – and unsolvable. Many don’t realise but the ozone crisis was the single most threatening to life on Earth – the one near miss. Although it was of course science that designed the harmful chemicals – we owe it to other scientists [and why not acknowledge climatology?] to keep us safe – and to geopolitics for showcasing international environmental cooperation can in fact be achieved – to great success: the Montreal Protocol – and the series of subsequent updates of this special UN climate treaty.
Despite the success of these environmental summits in mitigating the source of the problem, emissions of CFCs and comparable chemicals, we are still stuck with the fact that many of these gassy agents have very long atmospheric lifetimes.
The possible backlash of having a double crisis
This means the ozone crisis isn’t over. And before the last CFCs and HCFCs are phased out – it could even become worse. That’s because paradoxically a rise in greenhouse gas concentrations could lead to a lowering of stratospheric temperatures. Almost all GHGs are in the troposphere, that’s below the layer with the highest ozone concentrations. So while the GHGs keep the Earth’s surface warm, they also help isolate the much thinner part of the atmosphere above it.
And as long as catalytic breakdown components are plentiful up high, the longer the polar springs will experience temperatures below -90 C, the more polar stratospheric clouds could form, the more often ozone holes could pop up.
Such holes can migrate, by the way – so it’s not necessarily just polar bears that will be walking around with an extra spring tan.
© Rolf Schuttenhelm | www.bitsofscience.org